Monitoring mechanical heart properties

Abstract

In a method and system for monitoring mechanical properties of a heart in a subject, multiple cardiogenic impedance values reflective of the impedance of the heart in connection with a transition from inhalation to exhalation in the subject are determined. Correspondingly, multiple cardiogenic impedance values reflective of the impedance of the heart in connection with a transition from exhalation to inhalation are determined. The impedance values are collectively processed to form a trend parameter. The value determination and processing is performed over several respiratory cycles spaced apart in time to form a plurality of trend parameters over time. The mechanical properties of the heart are monitored by processing these different trend parameters. The data collection and optionally at least a part of the data processing is performed by an implantable medical device.

I claim as my invention: 
     
       1. A method of monitoring mechanical properties of a heart in a subject, comprising the steps of:
 a) determining a first set of multiple cardiogenic impedance values reflective of the impedance of said heart during a defined period of a heart cycle occurring in connection with a transition from inhalation to exhalation in said subject; 
 b) determining a second set of multiple cardiogenic impedance values reflective of the impedance of said heart during said defined period of a heart cycle occurring in connection with a transition from exhalation to inhalation in said subject; 
 c) collectively processing with a data processor said multiple cardiogenic impedance values of said first set as a function of said second set to determine a relationship between the first and second set and analyzing the relationship between the first and second sets to form a trend parameter representative of respiratory effect on said cardiogenic impedance values; 
 d) repeating said determining steps a), b) and processing step c) to form a plurality of trend parameters over time; and 
 e) monitoring said mechanical properties of said heart by processing said plurality of trend parameters. 
 
     
     
       2. The method according to  claim 1 , wherein step a) comprises:
 applying a first current signal or a first voltage signal to at least a portion of said heart during a first portion of a respiratory cycle; 
 measuring a first resulting voltage signal or a first resulting current signal over at least a portion of said heart during said first portion of said respiratory cycle; and 
 generating said first set of multiple cardiogenic impedance values based on said first current signal and said first resulting voltage signal or said first voltage signal and said first resulting current signal; and wherein step b) comprises: applying a second current signal or a second voltage signal to at least a portion of said heart during a second portion of said respiratory cycle; measuring a second resulting voltage signal or a second resulting current signal over at least a portion of said heart during said second portion of said respiratory cycle; and generating said second set of multiple cardiogenic impedance values based on said second current signal and said second resulting voltage signal or said second voltage signal and said second resulting current signal. 
 
     
     
       3. The method according to  claim 1 , wherein step c) comprises the steps of: plotting said multiple cardiogenic impedance values of said second set as a function of said multiple cardiogenic impedance values of said first set to obtain multiple plot points; and generating said trend parameter by processing said multiple plot points. 
     
     
       4. The method according to  claim 3 , wherein said generating step comprises the steps of: fitting an ellipse to said multiple plot points; and generating said trend parameter as a parameter being representative of said ellipse. 
     
     
       5. The method according to  claim 3 , wherein said generating step comprises the steps of: fitting a straight line to said multiple plot points; generating said trend parameter as a parameter being representative of said straight line. 
     
     
       6. The method according to  claim 1 , wherein step e) comprises plotting said plurality of trend parameters to display any changes of said mechanical properties of said heart. 
     
     
       7. The method according to  claim 6 , wherein said changes of said mechanical properties are due to an ischemic heart disease, progression of heart failure or poor inter-chamber synchronization of said heart. 
     
     
       8. A method of monitoring mechanical properties of a heart in a subject, comprising the steps of:
 a) determining a first set of multiple cardiogenic impedance values reflective of the impedance of said heart in connection with a transition from inhalation to exhalation in said subject; 
 b) determining a second set of multiple cardiogenic impedance values reflective of the impedance of said heart in connection with a transition from exhalation to inhalation in said subject: 
 c) collectively processing with a data processor said multiple cardiogenic impedance values of said first set as a function of said second set to determine a relationship between the first and second set and analyzing the relationship between the first and second sets to form a trend parameter representative of respiratory effect on said cardiogenic impedance values; 
 d) repeating said determining steps a), b) and processing step c) to form a plurality of trend parameters over time; 
 e) monitoring said mechanical properties of said heart by processing said plurality of trend parameters; 
 f) identifying a first heart cycle occurring in connection with said transition from inhalation to exhalation; and 
 g) identifying a second heart cycle occurring in connection with said transition from exhalation to inhalation; and wherein step a) comprises determining multiple cardiogenic impedance values reflective of the impedance of said heart during at least a portion said first heart cycle, and wherein step b) comprises determining multiple cardiogenic impedance values reflective of the impedance of said heart during at least a portion of said second heart cycle. 
 
     
     
       9. The method according to  claim 8 , further comprising the step of:
 h) generating a signal of multiple respiratory impedance values of said subject; and wherein step f) comprises identifying said first heart cycle as a heart cycle occurring in connection with a maximum value of said respiratory impedance signal during a respiration cycle, and wherein step g) comprises identifying said second heart cycle as a heart cycle occurring in connection with a minimum value of said respiratory impedance signal during said respiration cycle. 
 
     
     
       10. The method according to  claim 9 , wherein step f) comprises identifying said first heart cycle as a heart cycle coinciding with or being closest in time to said maximum value of said respiratory impedance signal during said respiration cycle and wherein step g) comprises identifying said second heart cycle as a heart cycle coinciding with or being closest in time to said minimum value of said respiratory impedance signal during said respiration cycle. 
     
     
       11. A system for monitoring mechanical properties of a heart in a subject, said system comprising:
 a data processor that generates a plurality of trend parameters representative of respiratory effect on cardiogenic impedance values by, for each trend parameter, collectively processing multiple cardiogenic impedance values reflective of the impedance of said heart during a defined period of a heart cycle occurring in connection with a transition from inhalation to exhalation in said subject as a function of multiple cardiogenic impedance values reflective of the impedance of said heart during said defined period of a heart cycle occurring in connection with a transition from exhalation to inhalation in said subject to determine a relationship between the first and second set and analyzing the relationship between the first and second sets to form the trend parameters; and 
 a property monitor that monitors said mechanical properties of said heart by processing said plurality of trend parameters. 
 
     
     
       12. The system according to  claim 11 , wherein the data processor is adapted to generate a plurality of first sets, each first set comprising multiple cardiogenic impedance values reflective of the impedance of said heart in connection with said transition from inhalation to exhalation in said subject, the data processor being further adapted to determine a plurality of second sets, each second set comprising multiple cardiogenic impedance values reflective of the impedance of said heart in connection with said transition from exhalation to inhalation of said subject. 
     
     
       13. The system according to  claim 12 , further comprising: a current applier that applies a current signal or a voltage signal to at least a portion of said heart; and a voltage measurer that measures a resulting voltage signal or a resulting current signal over at least a portion of said heart, and wherein said data processor generates multiple cardiogenic impedance values based on said current signal and said resulting voltage signal or said voltage signal and said resulting current signal. 
     
     
       14. The system according to  claim 11 , wherein said data processor comprises: a data plotter that plots said multiple cardiogenic impedance values reflective of the impedance of said heart in connection with said transition from exhalation to inhalation as a function of said multiple impedance values reflective of the cardiogenic impedance of said heart in connection with said transition from inhalation to exhalation to obtain multiple plot points; and a parameter generator that generates a trend parameter by processing said multiple plot points. 
     
     
       15. The system according to  claim 14 , wherein said parameter generator i) fits an ellipse to said multiple plot points and ii) generates said trend parameter as a parameter being representative of said ellipse. 
     
     
       16. The system according to  claim 14 , wherein said parameter generator fits a straight line to said multiple plot points and ii) generates said trend parameter as a parameter being representative of said straight line. 
     
     
       17. The system according to  claim 11 , wherein said property monitor plots said plurality of trend parameters on a connected display screen to display any changes of said mechanical properties of said heart. 
     
     
       18. A system for monitoring mechanical properties of a heart in a subject, said system comprising:
 a data processor that generates a plurality of trend parameters representative of respiratory effect on cardiogenic impedance values by, for each trend parameter, collectively processing multiple cardiogenic impedance values reflective of the impedance of said heart in connection with a transition from inhalation to exhalation in said subject as a function of multiple cardiogenic impedance values reflective of the impedance of said heart in connection with a transition from exhalation to inhalation in said subject to determine a relationship between the first and second set and analyzing the relationship between the first and second sets to form the trend parameters; 
 a property monitor that monitors said mechanical properties of said heart by processing said plurality of trend parameters; 
 an identification unit that i) identifies, for each first set, a first heart cycle of a respiratory cycle occurring in connection with said transition from inhalation to exhalation and ii) identifies, for each second set, a second heart cycle of said respiratory cycle occurring in connection with said transition from exhalation to inhalation. 
 
     
     
       19. The system according to  claim 18 , wherein said data processor i) determines, for each first set, multiple cardiogenic impedance values reflective of the impedance of said heart during at least a portion of said first heart cycle, and ii) determines, for each second set, said multiple cardiogenic impedance values reflective of the impedance of said heart during at least a portion of said second heart cycle. 
     
     
       20. The system according to  claim 19 , further comprising a signal generator adapted to generate a signal of multiple respiratory impedance values of said subject, and an identification unit adapted to identify for each first set, said first heart cycle as a heart cycle occurring in connection with a maximum value of said respiratory impedance signal during a respiration cycle, and for each second set, said second heart cycle as a heart cycle occurring in connection with a minimum value of said respiratory impedance signal during said respiration cycle. 
     
     
       21. The system according to  claim 20 , wherein said identification unit i) identifies, for each first set, said first heart cycle as a heart cycle coinciding with or being closest in time to said maximum value of said respiratory impedance signal during said respiration cycle and ii) identifies, for each second set, second heart cycle as a heart cycle coinciding with or being closest in time to said minimum value of said respiratory impedance signal during said respiration cycle. 
     
     
       22. An implantable medical device comprising: a system that i) determines a first set of multiple cardiogenic impedance values reflective of the impedance of a heart during a defined period of a heart cycle occurring in a subject in connection with a transition from inhalation to exhalation in said subject, and ii) determines a second set of multiple cardiogenic impedance values reflective of the impedance of said heart during said defined period of a heart cycle occurring in connection with a transition from exhalation to inhalation of said subject; and a data processor that generates decision support information useful in monitoring mechanical properties of said heart by collectively processing said first set of multiple cardiogenic impedance values as a function of said second set of multiple cardiogenic impedance values to determine a relationship between the first and second set and analyzing the relationship between the first and second sets to form the trend parameters.